The invention relates to a transport roller for the vacuum treatment of substrates, in particular for the conduct of coating and/or etching processes involving planar substrates such as architectural glass, solar cells and so forth. These processes are generally conducted under sub-atmospheric pressure, if necessary in the presence of a process gas, for instance an inert gas or a reactive gas, and in some cases under high temperatures, for example 600 or 800° C.
The transport rollers installed in a vacuum coating system are available in diverse forms and different materials. For example, interconnected transport rollers supported on two sides and powered on one or both sides are known. Furthermore, unconnected transport rollers arranged in pairs exist, which only support the substrate on both sides and transport it.
To transport, in particular, planar substrates through process systems in which these processes are taking place, transport systems are known which comprise an arrangement of transport rollers arranged in tandem transversely to the transport direction of the substrates, and rotatable supported on their ends, wherein at least some of the transport rollers can be powered. The substrates are placed onto the transport plane formed by the transport rollers and moved through the process system in the transport direction by rotating the transport rollers. In so doing, the substrates are moved past treatment systems, for example, systems for removing a surface layer from the substrates or systems for depositing a coating material on the surface of the substrates, so that the desired treatment processes are carried out.
Depending on the intended use, the transport rollers can be made of metallic materials, for example stainless steel or aluminum, or of non-metallic materials, for example industrial ceramics such as aluminum oxide, silicon oxide and so on. For transport rollers made of ceramic materials, it is further known that the ends on which the transport rollers are rotatably supported are provided with so-called end caps made of metallic materials.
The surface “hardness” of all listed roller materials is similar to that of the substrates to be transported. In the process, the buffing of the substrate edges generates loud noises and additional stress on the substrate, especially if the substrates are not completely flat or if the distances between the rollers are large due to the design (e.g. between two chambers or in the region of the chamber valve). This is particularly problematic in connection with accelerating runs and with thin or brittle substrates and can lead to substrate rupture. This situation results in prolonged down times, in particular with hot vacuum systems and, hence, to high losses in production.
The purpose of the heaters installed in a vacuum coating system is to set required temperature profiles on the substrate. Stable substrate temperatures are desirable in order to deposit layers with optimal properties. Especially in horizontal coating systems, the substrate is transported through the system on transport rollers. The thermal energy generated by the installed heaters is in part also transmitted to the transport rollers. If the substrate transport is impaired, above average heat input by means of heaters or coating sources into the transport rollers is possible for approximately 10 minutes. As a result, high local temperature gradients may occur in the transport roller, causing deformation (metal) or breakage (ceramic) with roller temperatures of 250° C. and higher.
The heat in particular introduced into the outer roller areas is removed through thermal conduction in the rollers and can result in the damage of temperature-sensitive assemblies of the transport system, unless they have a sufficiently temperature-sensitive design. In order to limit the heat input into the transport rollers, the lower heaters can be arranged between the transport rollers. The substrates shield the transport rollers from the upper heaters, thus preventing the heat input from this direction. However, this procedure is ineffective in the event that the system is operated with no load (e.g. conditioning of an empty chamber). In that case, the heat is mainly introduced by the upper heaters which can radiate onto the transport rollers unhindered if the substrate is missing.
One aspect of the invention is to reduce the heat input into the transport rollers and the thermal exposure of heat-sensitive assemblies.
In order to protect the substrates from being damaged because of scratching during the transport, the transport rollers can be provided with a plurality of cuffs or O-rings made of permanently elastic materials such as rubber, Viton or similar material, distributed across the entire length, in order to reduce the contact area between the transport cylinder and the substrate. Nevertheless, it is extremely difficult to achieve a completely scratch-free transport of the substrates. A further disadvantage is that the material of the O-ring does not allow the use at higher temperatures, the substrate is only supported punctiformally and the service life is very limited.
Due to the limited thermal durability of rubber, Viton and similar materials as well as the high costs of other elastomers, the object of the invention is to find a suitable replacement material or replacement design to substitute for O-rings made of elastomeric materials. Therefore, a replacement of traditional O-rings will be proposed, with comparable elastic properties to known elastomers. Furthermore, the friction coefficient with respect to glass should be analogous to that for the combination of a traditional elastomer and glass.
To solve the problem that particles of the coating material are deposited not only on the substrate during coating processes, but also on the transport rollers, with the result that the transport rollers need to be exchanged after a certain period of operation, it was proposed in DE 10 2008 022 689 A1 to provide an enveloping element enveloping the surface area of the roll body of a transport roller for the vacuum treatment of substrates, wherein the enveloping element is mounted on the surface area and can be made for example of a fabric.
Fabric is the generic term for manually or mechanically manufactured products of the weaver's trade or other textile areal structures having at least two thread systems crossed at a right angle or almost at a right angle. The threads running in longitudinal direction are referred to as warp or beam threads. The diagonal threads are called picks or weft threads. The areas are connected with the thread crossing connection type. Thread crossing does not mean that the threads are placed on top of each other crossed, but that the threads are passing above and underneath the diagonal threads at a certain rhythm (known as weave). In order for a fabric to have adequate non-slip properties, the warp and weft threads are usually weaved relatively dense. With a few exceptions, the fabrics therefore have a tight fabric appearance.
Known metal fabrics are manufactured with mesh sizes ranging between 0.06 and 4 mm, fabric widths of up to 6000 mm as yard ware in rolls, in the weaving modes smooth or linen texture, braiding, armored braiding, body braiding, wherein wire diameters between 0.16 and 2 mm are used.
If the proposed transport cylinder is used in a coating process, the particles of the coating material are no longer deposited on the roll body but rather on the enveloping element covering the roll body. In contrast, if the transport cylinder is used for stripping processes, the stripping will not affect the roll body, but the enveloping element. If necessary, said type of enveloping element can easily and quickly be detached from the roll body and exchanged for a new enveloping element. There is no need to clean the cylinder element and as a result, the risk of damage during the cleaning can be prevented as well.
However, it has been demonstrated that the risk of arcing cannot be completely excluded with the use of said types of fabrics for the mentioned purpose, for example, in plasma-assisted processes. Furthermore, these types of fabrics have a relatively high thermal conductivity which can lead to an undesirable uneven temperature distribution on the substrate. Finally, fabrics are not very flexible due to their relatively smooth and tight surface, on the one hand, and slippage between the substrate and the surface of the fabric cannot be completely excluded, on the other hand.
For these reasons, a further aspect of the invention is to find a suitable replacement material or a replacement design to substitute for enveloping elements made of fabric, having similar elastic properties as known elastomers, allowing a slip-free transport of the substrates while not resulting in undesirable arcing.